Thursday, June 9, 2011

Just when you thought it was safe to empty your sandbags, turns out it is not. For many residents of the Midwest, the US Army Corps of Engineers "Flood Threat Assessment" provides nothing more than worrisome news:

"The Kansas City District U.S. Army Corps of Engineers' reach of the Missouri River, which extends from Rulo, Nebraska to the Mississippi River, will experience flood stages similar to 2010 levels, possibly greater. We caution communities and levee districts along the river to prepare for flood fight and possible evacuation."

So what the heck is this all about? Where is all the water coming from?

The headwaters of the "Mighty Mo" is high in the Rocky Mountains, at an elevation of 4,045 feet. About 25 miles northwest of Bozeman, Montana, the Madison and Jefferson Rivers come together, creating the Missouri River. From this point, the Missouri River will flow 2,320.7 miles to its confluence with the Mississippi River at St. Louis.

About 15 miles down stream, the Missouri encounters the first of many dams, placed to control flooding hundreds of miles down stream.

Toston Dam is operated by the Montana Department of Natural Resources and Conservation (DNRC.)

Concrete gravity dam

705 feet long

56 feet high

Completed in 1940

Retrofitted to include a 10 megawatt generating capability in 1989.

The Toston Dam is the first in a series of monitoring stations, used to calculate an "Exceedance Forecast" by the US Department of Agriculture's Natural Resource Conservation Service. This forecast is based on "Runoff Components" draining into the Missouri Basin.

The numbers they generated came as no surprised, given the deeper than normal snow pack in the Rockies, and unseasonable rainfall. This is the actual forecast, and it is not a pretty sight:

The "Exceedance Forecast" is fueled by 140 percent of normal snow melt runoff into the lakes, along with record spring precipitation on top of that, essentially filling up the flood storage in the Missouri River lakes and necessitating record releases. The high releases are expected to last all summer and into the fall and winter.

In the Missouri River Basin, there are more than 80 flood control structures on the dozens and dozens of tributaries that feed the Missouri River. Including the State operated Toston Dam, there are a total of 15 flood control structures, from headwaters to St. Louis, to manage flood control:

Federal, US Department of Interior, Bureau of Reclamation:

Canyon Ferry

Between Canyon Ferry and Fort Peck, there are seven "non-Federal" dams, owned and operated by PPL Montana, (Pennsylvania Power & Light) a private power company:

In researching this series of dams, I discovered the Fort Peck Dam is fascinating example of extreme engineering.

With the proposed length of the dam more than six miles, it was quickly determined that dump trucks would not be practical for moving the estimated 125,626,000 cubic yards of earth required to construct the dam.

So a process called "hydraulic earth fill" was used to constructed the dam. This required a fleet of dredges and miles of pipeline. In essence, the Missouri River bottom and banks were dredged and pumped through pipe lines to construct the dam.

In addition to the dredges, a railroad trestle was built to bring in material, dumped off the trestle with side dump cars. It is an amazing story way too complex to relate here. But if you are interested, there is a website chock full of photographs, documenting the building of Fort Peck Dam.

Water Flow: 50,000 cf/s (previous record, 45,000 cf/s in 1975. Rain and an increase in local water runoff have prompted the U.S. Army Corps of Engineers to increase the water flow at the Fort Peck Reservoir.

On Friday, June 10 the water flow rate will increase by 5,000 cubic feet per second (cf/s) to 55,000 cf/s. The increased flow should balance the water levels between Fort Peck and Garrison Dam in North Dakota.

Water Flow: This is the emergency flow the Corps of Engineers released from Lake Oahe. This is what is caused the flooding in the cities of Pierre and Fort Pierre in late May 2011. This is what water traveling near 60 miles per hour, 88,000 cubic feet/second, looks like up close!Big Bend Dam

Water Flow: Friday, June 3. This was the first time in the history of the dam, completed in 1963, that the spillway gates have been opened to pass floodwaters. The process took more than 20 minutes to complete. However, this neato video, shot by South Dakota Public Broadcasting, speeds the process up considerably!

A special viewing area on the south side of the spillway was be opened up as a vantage point for the public and media to photograph, view or shoot. The gates opened Friday to release an additional 15,000 cf/s, bringing the total release out of Big Bend Dam to 100,000 cf/s.

After Friday's opening, the gates will be raised daily to allow for additional flow through the spillway. On Tuesday, June 7 the gates reached their peak, allowing for a target spillway release of 65,000 cf/s. When combined with the 85,000 cf/s of water being released through the powerhouse, an historic 150,000 cf/s will be released into Lake Francis Case, behind Fort Randall Dam.

Water Flow: The Corps of Engineers began releasing 150,000 cfs flow from Gavins Point Dam into the lower Missouri River system. The previous record release level was 70,000 cubic feet/second.

Strange Structures

Perhaps you have noticed in the photographs, some dams feature tall structures resembling grain elevators.

The purpose of these surge tanks is to prevent water hammer from damaging the dam. "Water hammer," is a phenomenon that occurs when water, passing though a pipe or conduit, is suddenly stopped. We remember from high school physics that water cannot be compressed.

When a tunnel full of water, moving at 5 to 10 miles per hour, is suddenly stopped by a valve controlling water flow into the power house (above) a powerful shock wave - water hammer - moves back through the column of water, with enough energy to inflict serious damage if it cannot be disbursed or absorbed.

The surge tank absorbs the water hammer shock wave, thus protecting the structure from damage. Not all structures require this safe guard. They are installed when there is a significant distance between the intake and the turbine.

[Ed Note: There is a YouTube video showing a catastrophic failure of a dam turbine in Russia, in August of 2009. The video incorrectly attributes the explosion as being the result of "water hammer." It was not. It was the failure of the bolts securing the turbine into the powerhouse floor, which caused launched a thousand ton turbine 50 feet into the air like a bottle rocket, killing dozens.]

Well, that completes my armchair assessment of the flood control structures built into the Missouri River System and the steps being taken to deal with an aggressive runoff originating more than 2,000 miles away, high in the Rocky Mountains.

So the question is, "As the "Mighty Mo" joins "Old Man River" at Saint Louis, will this result in another round of high water affecting the Mississippi?"

Indeed, I co-owned Media Resources, Inc. in Vancouver Washington for a number of years.

When I began writing this Blog, the focus was on second-generation diesel power. As a young lad living in Prince Rupert, from 1957 through 1959, I began learning about diesel-electric locomotives. The Twilight of steam.

While my core interest remains unchanged, I have changed. Therefore, from time to time, I present subject material that I find absolutely interesting, hopefully you will too!